1. Technical Field
Example embodiments generally relate to an optical scanning device and an image forming apparatus using an electrophotographic method, such as a copier, a printer, a facsimile machine, and a multifunction apparatus that combines the functions of the copier, the printer, and the facsimile machine.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image bearing member (e.g., a photoconductor). An optical scanning device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data. The electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor. A transfer device transfers the toner image formed on the photoconductor onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
In such an image forming apparatus, the optical scanning device generally includes a light source, a polygon mirror serving as a deflector, an fθ lens, a long lens, and a reflection mirror serving as a reflective optical element. A light beam emitted from the light source is deflected and scanned at a constant angular speed by the polygon mirror being rotated, and enters the fθ lens. The fθ lens focuses the light beam in a main scanning direction and corrects the light beam such that the light beam may scan the photoconductor at a constant speed. Subsequently, the thus-corrected light beam enters the long lens, and is focused in a sub-scanning direction. At this time, an optical surface tangle error of the polygon mirror is also corrected. Thereafter, the light beam passing through the long lens is deflected by the reflection mirror, and irradiates the photoconductor.
In the above-described optical scanning device, a curve and a tilt may appear in a scanning line of the light beam irradiating the photoconductor due to curvature of field in the reflective optical element, deformation of a housing of the optical scanning device, thermal deformation of components provided in the optical scanning device caused by heat from a polygon motor, misalignment of the photoconductor, and so forth. When the curve and the tilt appear in the scanning line, a proper latent image corresponding to image data may not be formed on the photoconductor, and consequently, a proper image may not be obtained.
In a tandem type full-color image forming apparatus, toner images of different colors are respectively formed on a plurality of the photoconductors, and the toner images are superimposed on one another to form a full-color image. Accordingly, a user may more easily notice image irregularity in the full-color image caused by curves and tilts in the scanning lines of the light beams irradiating the respective photoconductors.
In other words, the user may rarely notice the image irregularity in a single-color image caused by a slight tilt and curve in the scanning line of the light beam. However, the curves and the tilts in the scanning lines of the light beams irradiating the respective photoconductors cause a color shift in the full-color image formed by the tandem type full-color image forming apparatus, and even a slight color shift may be easily noticed by the user as the image irregularity.
To solve such a problem, one example optical scanning device is proposed in which both a curve adjustment unit for bending a long lens to adjust a curve in a scanning line and a tilt adjustment unit for rotating a long lens to change a position of the long lens and adjust a tilt of the scanning line are provided.
Moreover, to meet demand for reduction in a number of components and downsizing of the optical scanning device, another example optical scanning device including a scanning lens having both characteristics of the fθ lens and the long lens has been widely used. In such an optical scanning device, a light beam emitted from a light source is deflected by a polygon mirror being rotated, and the thus deflected light beam enters the scanning lens. Subsequently, the scanning lens focuses the light beam in a main scanning direction and a sub-scanning direction such that the light beam irradiates the photoconductor to form a spot thereof having a predetermined or desired shape, and corrects the light beam to be scanned at a constant speed. At this time, an optical surface tangle error of the polygon mirror is also corrected. Thereafter, the light beam passing through the scanning lens is deflected by a reflection mirror and irradiates the photoconductor.
Because the optical scanning device including the scanning lens does not include the long lens, the curve and the tilt in the scanning line may not be adjusted by bending and rotating the long lens in contrast to the example optical scanning device including the long lens described above. Therefore, in the optical scanning device including the scanning lens, the tilt and the curve in the scanning line may be adjusted by bending and rotating the scanning lens having the characteristics of the long lens.
However, an angle of incidence of the light beam deflected by the polygon mirror on the scanning lens differs depending on a position of incidence of the light beam in the main scanning direction. Thus, the scanning lens focuses the light beam differently depending on each position of incidence of the light beam in the main scanning direction.
In other words, when the scanning lens is bent to adjust the curve in the scanning line and rotated to adjust the tilt of the scanning line, the position of incidence of the light beam is changed. As a result, the light beam entering the scanning lens may not be properly focused, and the irradiated light beam does not form a spot having a predetermined or desired shape on the photoconductor. Furthermore, dot latent images formed on each of the photoconductors are shifted toward the main scanning direction. Consequently, higher quality images may not be obtained.